A Tour of the Cell

Page
9

Intermediate filaments are fibers with diameters in a middle range

Slide 71

Table 6-1

10 µm

10 µm

10 µm

Column of tubulin dimers

Tubulin dimer

Actin subunit





25 nm

7 nm

Keratin proteins

Fibrous subunit (keratins coiled together)

8–12 nm

Slide 72

Table 6-1a

10 µm

Column of tubulin dimers

Tubulin dimer





25 nm

Slide 73

Table 6-1b

Actin subunit

10 µm

7 nm

Slide 74

Table 6-1c

5 µm

Keratin proteins

Fibrous subunit (keratins

coiled together)

8–12 nm

Slide 75

Microtubules

Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns long

Functions of microtubules:

Shaping the cell

Guiding movement of organelles

Separating chromosomes during cell division

Slide 76

Centrosomes and Centrioles

In many cells, microtubules grow out from a centrosome near the nucleus

The centrosome is a “microtubule-organizing center”

In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring

Slide 77

Fig. 6-22

Centrosome

Microtubule

Centrioles

0.25 µm

Longitudinal section of one centriole

Microtubules

Cross section

of the other centriole

Slide 78

Cilia and Flagella

Microtubules control the beating of cilia and flagella, locomotor appendages of some cells

Cilia and flagella differ in their beating patterns

Video: Chlamydomonas

Video: Paramecium Cilia

Slide 79

Fig. 6-23

5 µm

Direction of swimming

(a) Motion of flagella

Direction of organism’s movement

Power stroke

Recovery stroke

(b) Motion of cilia

15 µm

Slide 80

Cilia and flagella share a common ultrastructure:

A core of microtubules sheathed by the plasma membrane

A basal body that anchors the cilium or flagellum

A motor protein called dynein, which drives the bending movements of a cilium or flagellum

Animation: Cilia and Flagella